WhichBookmakerCalculator · 2026-09-28
Matched betting calculator
Enter the back bet, the lay odds and the exchange commission. You get the lay stake that equalises both outcomes, the liability you need in your exchange account, and the guaranteed result whichever side wins — for a normal qualifying bet and for a stake-not-returned free bet, which use different formulas.
18+.
How the lay odds change your result
The same bet at a spread of lay odds around the one you entered, so you can see how much a better or worse price on the exchange actually moves the outcome.
| Lay odds | Lay stake | Liability | Result |
|---|---|---|---|
How the calculator works
A qualifying bet backs a selection at the bookmaker and lays the same outcome at the exchange, so one side must win. Most calculators size the lay stake as back stake × back odds ÷ lay odds, which is only correct at zero commission. With commission c on the exchange, the lay stake that equalises both results is L = (back stake × back odds) ÷ (lay odds − c), where c is expressed as a decimal share of the lay odds.
A stake-not-returned free bet uses a different formula, because you keep no stake if the back bet wins: only the winnings are backed. The equalising lay stake is L = (free bet × (back odds − 1)) ÷ (lay odds − c). This is why a free bet is never worth its full face value — the extraction rate depends on both the odds and the commission, and it is usually 70% to 80%, not 100%.
Liability is what the exchange holds from your account while the lay bet is open: lay stake × (lay odds − 1). It needs to be sitting in your exchange balance before you place the lay side, and it is returned to you, adjusted by the result, once the event settles.
Getting an accurate lay stake
- Lay odds move between backing and laying. Use the current exchange price, not the one you saw a minute ago, or the equalisation breaks and one side pays more than the other.
- Commission is charged on net winnings from the lay side only, never on a loss. A 6% commission at Betfair costs more than a 2% flat rate at Smarkets or Matchbook on the same lay stake.
- Free bets extract best at longer odds: around 30% of face value backed at 1.5, but 70% to 80%+ from about 4.0 upward, because the winnings are large relative to the liability you need to cover. Chase free bet offers on markets priced 4.0 or longer where you can.
- Round the lay stake to what the exchange accepts (usually the nearest whole unit of its minimum), and re-check the price immediately before placing it — a stale price is the most common source of an unmatched qualifying loss.
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Frequently asked questions
How do I calculate the lay stake for matched betting?
Lay stake = (back stake × back odds) ÷ (lay odds − commission), where commission is entered as a decimal share of the lay odds (2% commission is 0.02). For example, backing £10 at 3.0 and laying at 3.1 with 2% commission gives a lay stake of (10 × 3.0) ÷ (3.1 − 0.02) = £9.74. Ignoring commission, as many simple calculators do, would give £9.68 instead — a small but real difference in your liability.
Why is my qualifying bet losing a little money either way?
That is normal and expected. Because the exchange charges commission on lay winnings but the bookmaker pays nothing on the back side, the two outcomes cannot be made to pay exactly the same, and the small gap — usually 1% to 3% of the back stake — is the "qualifying loss" that buys you eligibility for a free bet offer worth far more than the loss.
Why does a free bet only pay out a fraction of its face value?
Because you only back the winnings, not the stake, so what you can lay off is small relative to the liability it creates at short odds. The extraction rate rises sharply with the odds: roughly 33% backed at 1.5, about 66% at 3.0, and 70% to 90% from 4.0 upward at typical exchange commission. This is why serious matched bettors chase free bet offers on longer-priced markets and use low-commission exchanges rather than accepting whatever price a bookmaker's offer happens to apply to.
Which exchange has the lowest commission?
As of 2026, Smarkets and Matchbook both charge a flat 2% on net winnings (Matchbook splits it into 0.75% for orders that sit in the book and 1.5% for orders that take an existing price), while Betfair's standard commission is 6%, with a lower tier for high-volume accounts. New-user 0% commission promotions appear periodically on the smaller exchanges and are worth using while they last, since the calculator above shows how much they improve your result.